Process for making an ink jet ink

ABSTRACT

A process for making an ink jet ink comprising: 
     a) providing a dispersion containing a pigment, an alcohol carrier and an amine-terminated polyether dispersant; 
     b) mixing the pigment dispersion with rigid milling media less than 100 μm; 
     c) introducing the mixture of step (b) into a mill; 
     d) milling the mixture from step (c) until the pigment particle size is below about 100 nanometers; 
     e) separating the milling media from the mixture milled in step (d); and 
     f) diluting the mixture from step (e) to obtain an ink jet ink having a pigment concentration suitable for ink jet printers.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned copending U.S. patent applicationSer. No. 09/170,660, filed Oct. 13, 1998, U.S. Pat. No. 6,053,438entitled “Process for Making an Ink Jet Ink”, by Romano et al., and U.S.patent application Ser. No. 09/468,412 filed concurrently herewith,entitled “Ink Jet Ink”, by Guistina et al., the teachings of which areincorporated herein by reference.

FIELD OF THE INVENTION

This application relates to a process for making an ink jet ink using analcohol carrier and a particular dispersant to produce a dispersioncharacterized by nanometer-size pigment particles.

BACKGROUND OF THE INVENTION

Ink jet printing is a non-impact method for producing images by thedeposition of ink droplets on a substrate (paper, transparent film,fabric, etc.) in response to digital signals. Ink jet printers havefound broad applications across markets ranging from industrial labelingto short run printing to desktop document and pictorial imaging. Theinks used in ink jet printers are generally classified as eitherdye-based or pigment-based.

In pigment-based inks, the colorant exists as discrete particles. Thesepigment particles are usually treated with addenda known as dispersantsor stabilizers which serve to keep the pigment particles fromagglomerating and settling out of the carrier. Such a dispersant isnecessary to produce a colloidally stable mixture and an ink that can be“jetted” reliably without clogging the print head nozzles.

Dispersing agents in an ink jet ink have the dual function of helping tobreak down pigments to sub-micron size during the milling process and ofkeeping the colloidal dispersion stable and free from flocculation for along period of time. In general, dispersions suffer from poor colloidalstability due to particle agglomeration and/or sedimentation, thuslimiting the usefulness of the dispersions in inks.

Although a wide variety of dispersing agents are known for pigmented inkjet inks, they are not without certain problems. For example, manydispersing agents are very selective as far as being able to dispersepigments to sub-micron size. In many instances, each class of pigmentsmay require a specific dispersing agent. Another problem encounteredwith some polymeric dispersing agents is that they tend to impart anundesirably high viscosity to the resulting inks. Thus, there is acontinuing need for improved dispersing agents for pigmented inks,especially for non-aqueous inks.

Dispersing agents for non-aqueous ink jet inks previously used includemetal salts of styrene-acrylic copolymers, metal salts of sulfonatedstyrene-acrylic copolymers, phosphonium salts or quaternary ammoniumsalts of styrene-acrylic copolymers.

U.S. Pat. No. 5,679,138 relates to a process for preparing an ink jetink wherein the pigment particle size distribution obtained is quitesmall. There is a problem with this process, however, in that thecarrier medium is limited to water. It would be desirable to provide inkjet inks which employ non-aqueous carriers in order to avoid paperdeformation upon printing. However, dispersing agents commonly used foraqueous dispersions generally do not work in non-aqueous dispersions.

U.S. Pat. Nos. 5,837,046; 5,739,833 and 5,538,548 relate to ink jet inkscontaining various Disperbyk® dispersants used in a variety of carrierssuch as aliphatic hydrocarbons and dibasic esters. However, there is aproblem with these dispersants in that they do not provide very lowparticle size dispersions when used with alcohol carriers.

It is an object of this invention to provide a method for making anon-aqueous, pigment dispersion for an ink jet ink with a low particlesize in order to obtain better covering power and which would have lesstendency to clog the ink jet nozzles. It is another object of thisinvention to provide a method for making a non-aqueous, pigmentdispersion for an ink jet ink which employs a dispersant which enablesthe production of nanometer-size pigment particles.

SUMMARY OF THE INVENTION

These and other objects are achieved in accordance with this inventionwhich relates to a process for making an ink jet ink comprising:

a) providing a dispersion containing a pigment, an alcohol carrier andan amine-terminated polyether dispersant;

b) mixing the pigment dispersion with rigid milling media less than 100μm;

c) introducing the mixture of step (b) into a mill;

d) milling the mixture from step (c) until the pigment particle size isbelow about 100 nanometers;

e) separating the milling media from the mixture milled in step (d); and

f) diluting the mixture from step (e) to obtain an ink jet ink having apigment concentration suitable for ink jet printers.

The dispersant used in the process of the invention is highly effectivein reducing pigment particles to a size of less than about 100 nm whenmilled in the presence of very fine milling media. The resultingdispersion is characterized by nanometer-size pigment particles. Thedispersing agents employed are useful with a wide variety of pigments.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the ink jet ink composition used in the process of theinvention contains an amine-terminated polyether dispersant. Thedispersant is preferably used in a ratio of dispersant to pigment fromabout 0.1:1 to about 5:1. In a preferred embodiment, the ratio ofdispersant to pigment is from about 0.5:1 to about 2:1.

In a preferred embodiment of the invention, the amine-terminatedpolyether has the following formula:

where

R₁, R₄ and R₅ each individually represents a substituted orunsubstituted alkyl group having from 1 to about 6 carbon atoms;

R₂ represents hydrogen or a substituted or unsubstituted alkyl grouphaving from 1 to about 6 carbon atoms;

R₃ represents a substituted or unsubstituted alkyl group having from 1to about 10 carbon atoms or a substituted or unsubstituted aryl grouphaving from about 6 to about 10 carbon atoms;

x is from about 5 to about 100; and

y is from 1 to about 6.

In another preferred embodiment, R₁, R₄ and R₅ in the above formula eachindividually represents methyl or ethyl. In another preferredembodiment, R₂ is methyl. In yet another preferred embodiment, R₃ is amethyl-substituted aryl group. In still another preferred embodiment, xis from about 15 to about 45 and y is 2. An example of these dispersantswhich is commercially available is Disperbyk® BYK 182 from BYK-Chemie,USA.

In the present invention, any of the known pigments can be used.Pigments can be selected from those disclosed, for example, in U.S. Pat.Nos. 5,026,427; 5,086,698; 5,141,556; 5,160,370; and 5,169,436, thedisclosures of which are hereby incorporated by reference. The exactchoice of pigments will depend upon the specific color reproduction andimage stability requirements for the printer and application. Thepigment must be totally insoluble in the carrier. For four-colorprinters, combination of cyan, magenta, yellow, and black (CMYK)pigments should be used. An exemplary four color set isbis(phthalocyanyl-alumino)tetraphenyl-disiloxane cyan, quinacridonemagenta (C.I. Pigment Red 122), Hansa® Brilliant Yellow 5GX-02 (C.I.Pigment Yellow 74), and carbon black (C.I. Pigment Black 7).

As noted above, the pigment particle size obtained using this process isbelow about 100 nm. This figure is understood to mean the 50^(th)percentile value (half of the particles have a particle size below thatvalue and half are above). Particle size distributions can be measuredon diluted millgrind samples (about 50:1) using a Leeds & NorthropUltrafine Particle Analyzer (UPA).

The process of preparing inks from pigments commonly involves two steps:(a) a dispersing or milling step to break up the pigment to the primaryparticle, and (b) a dilution step in which the dispersed pigmentconcentrate is diluted with a carrier and other addenda to a workingstrength ink. In the milling step, the pigment is usually suspended in acarrier along with rigid, inert milling media less than about 100 μm.The dispersing agent is added at this stage. Mechanical energy issupplied to this pigment dispersion, and the collisions between themilling media and the pigment cause the pigment to deaggregate into itsprimary particles.

There are many different types of materials which may be used as millingmedia, such as glasses, ceramics, metals, and plastics. In a preferredembodiment, the grinding media can comprise particles, preferablysubstantially spherical in shape, i.e., beads consisting essentially ofa polymeric resin.

In general, polymeric resins suitable for use as milling media arechemically and physically inert, substantially free of metals, solventand monomers and of sufficient hardness and resilience to enable them toavoid being chipped or crushed during milling. Suitable polymeric resinsinclude crosslinked polystyrenes, such as polystyrene crosslinked withdivinylbenzene, styrene copolymers, polyacrylates such aspoly(methylmethacrylate), polycarbonates, polyacetals such as Derlin®vinyl chloride polymers and copolymers, polyurethanes, polyamides,poly(tetrafluoroethylenes), e.g. Teflon®, and other fluoropolymers, highdensity polyethylenes, polypropylenes, cellulose ethers and esters suchas cellulose acetate, poly(hydroxyethylmethacrylate), poly(hydroxyethylacrylate), silicone containing polymers such a polysiloxanes and thelike. The polymer can be biodegradable. Exemplary biodegradable polymersinclude poly(lactides), poly(glycolids) copolymers of lactides andglycolide, polyanhydrides, poly(imino carbonates),poly(N-acylhydroxyproline) esters, poly(palmitoyl hydroxyproline)esters, ethylene-vinylacetate copolymers, poly(orthoesters),poly(caprolactones), and poly(phosphazines). The polymeric resin canhave a density from 0.9 to 3.0 g/cm³. Higher density resins arepreferred inasmuch as it is believed that these provide more efficientparticle size reduction. Most preferred are crosslinked or uncrosslinkedpolymeric media based on styrene.

Milling can take place in any suitable grinding mill. Suitable millsinclude an airjet mill, a roller mill, a ball mill, an attritor mill anda bead mill. A high speed mill is preferred, such as those manufacturedby Morehouse-Cowles, Hockmeyer, or Premier Mills.

By high speed mill is meant a milling device capable of acceleratingmilling media to velocities greater than about 5 meters per second. Themill can contain a rotating shaft with one or more impellers. In such amill the velocity imparted to the media is approximately equal to theperipheral velocity of the impeller, which is the product of theimpeller rev/min and the impeller diameter. Sufficient milling mediavelocity is achieved, for example, in Cowles-type saw tooth impellerhaving a diameter of 40 mm when operated at about 6,000 to about 9,000rev/min. The preferred proportions of the milling media, the pigment,the carrier and dispersing agent can vary within wide limits and depend,for example, upon the particular material selected and the size anddensity of the milling media, etc.

Batch Milling

A slurry of <100 μm milling media, carrier, pigment, and dispersingagent(s) is prepared using simple mixing. This slurry may be milled inconventional high energy batch milling processes such as high speedattritor mills, vibratory mills, ball mills, etc. This slurry is milledfor a predetermined length of time to allow comminution of the activematerial to a minimum particle size. After milling is complete, thedispersion of active material is separated from the grinding media by asimple sieving or filtration.

The milling time can vary widely and depends upon the pigment,mechanical means and residence conditions selected, the initial anddesired final particle size, etc.

The carrier can be any of the alcohols such as isopropanol, methanol,ethanol, propanol, butanol, etc. Selection of a suitable alcohol carrierdepends on the requirements of the specific application, such asviscosity, surface tension, drying time of the pigmented ink jet ink,and the type of receiver on which the ink will be printed. The amount ofthe carrier employed is in the range of about 20 to 40 weight %,preferably about 25 to about 35 weight %, based on the total weight ofthe slurry.

Ink Preparation.

In general, it is desirable to make the pigmented ink jet ink in theform of a concentrated millgrind, which is subsequently diluted to theappropriate concentration for use in the ink jet printing system. Thistechnique permits preparation of a greater quantity of pigmented inkfrom the equipment. The millgrind is diluted with appropriate solvent toa concentration best for viscosity, color, hue, saturation density, andprint area coverage for the particular application.

In the case of organic pigments, the ink may contain up to about 30%pigment by weight, but will generally be in the range of about 0.1 to10%, preferably about 0.25 to about 5%, by weight of the total inkcomposition for most of the ink jet printing applications.

Acceptable viscosities, as determined using Brookfield apparatus andrelated methods are generally not greater than 20 centipoise, and arepreferably in the range of about 1 to 15 centipoise.

The ink has physical properties compatible with a wide range of ejectingconditions, i.e., driving voltages and pulse widths for thermal ink jetprinting devices, driving frequencies of the piezo element for either adrop-on-demand device or a continuous device, and the shape and size ofthe nozzle.

A humectant may be employed in the ink jet compositions used in theinvention to help prevent the ink from drying out or crusting in theorifices of the printhead. Examples of humectants which can be usedinclude monohydric alcohols with carbon chains greater than about 10carbon atoms such as decanol, dodecanol, oleoyl alcohol, stearoylalcohol, hexadecanol, eicosanol, polyhydric alcohols, such as ethyleneglycol, alcohol, diethylene glycol(DEG), triethylene glycol, propyleneglycol, tetraethylene glycol, polyethylene glycol, glycerol,2-methyl-2,4-pentanediol, 2-ethyl-2-hydroxymethyl-1,3-propanediol(EHMP),1,5pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol and thioglycol; loweralkyl mono- or di-ethers derived from alkylene glycols, such as ethyleneglycol mono-methyl or mono-ethyl ether, diethylene glycol mono-methyl ormono-ethyl ether, propylene glycol mono-methyl or mono-ethyl ether,triethylene glycol mono- methyl or mono-ethyl ether, diethylene glycoldi-methyl or di-ethyl ether, poly(ethylene glycol) monobutyl ether(PEGMBE), and diethylene glycol monobutylether(DEGMBE);nitrogen-containing compounds, such as urea, 2-pyrrolidinone,N-methyl-2-pyrrolidinone, and 1,3-dimethyl-2-imidazolidinone; andsulfur-containing compounds such as dimethyl sulfoxide andtetramethylene sulfone.

Polymeric binders can also be added to the ink employed in the inventionto improve the adhesion of the colorant to the support by forming a filmthat encapsulates the colorant upon drying. Examples of polymers thatcan be used include polyesters, polystyrene/acrylates, sulfonatedpolyesters, polyurethanes, polyimides and the like. The polymers may bepresent in amounts of from about 0.01 to about 15 percent by weight andmore preferably from about 0.01 to about 5 percent by weight based onthe total amount of components in the ink.

A biocide may be added to the ink composition employed in the inventionto suppress the growth of micro-organisms such as molds, fungi, etc. inaqueous inks. A preferred biocide for the ink composition employed inthe present invention is Proxel® GXL (Zeneca Specialties Co.) at a finalconcentration of 0.0001-0.5 wt. %.

Additional additives which may optionally be present in the ink jet inkcompositions employed in the invention include thickeners, conductivityenhancing agents, anti-kogation agents, drying agents, waterfast agents,dye solubilizers, chelating agents, binders, light stabilizers,viscosifiers, buffering agents, anti-mold agents, anti-curl agents,stabilizers and defoamers.

The ink jet inks provided by this invention are employed in ink jetprinting wherein liquid ink drops are applied in a controlled fashion toan ink receptive substrate, by ejecting ink droplets from plurality ofnozzles, or orifices, in a print head of ink jet printers.

Commercially available ink jet printers use several different methods tocontrol the deposition of the ink droplets. Such methods are generallyof two types: continuous stream and drop-on-demand.

In drop-on-demand systems, a droplet of ink is ejected from an orificedirectly to a position on the ink receptive layer by pressure createdby, for example, a piezoelectric device, an acoustic device, or athermal process controlled in accordance digital data signals. An inkdroplet is not generated and ejected through the orifices of the printhead unless it is needed. Ink jet printing methods, and relatedprinters, are commercially available and need not be described indetail.

The ink jet inks provided by this invention are employed in ink jetprinting wherein liquid ink drops are applied in a controlled fashion toan ink receptive layer substrate, by ejecting ink droplets from theplurality of nozzles, or orifices, in a print head of ink jet printers

Ink-receptive substrates useful in ink jet printing are well known tothose skilled in the art. Representative examples of such substrates aredisclosed in U.S. Pat. Nos. 5,605,750; 5,723,21 1; and 5,789,070 and EP813 978 A1, the disclosures of which are hereby incorporated byreference.

THE FOLLOWING EXAMPLES ILLUSTRATE THE UTILITY OF THE PRESENT INVENTION.EXAMPLE 1

Dispersion 1 (Invention)

A yellow dispersion was prepared by mixing the following Ingredients:

9.0 g Hansa® Brilliant Yellow 5GX-02 pigment (C.I. Pigment Yellow 74)(Hoechst Chem. Co.)

9.5 g Disperbyk® 182 dispersing agent (BYK-Chemie USA)

50.0 g isopropanol carrier (JT Baker Co.)

10 87.5 g 50 μm polymeric milling media (crosslinked polystyrene beads).

The above components were mixed and then milled in a 0.5 liter doublewalled vessel obtained from BYK-Gardner using a Series 2500 HVDispersator (an explosion-proof, high energy laboratory dispersator,manufactured by Premier Mill Corp.) with a 40 mm. Cowles-type toothedmilling blade rotating at about 6,400 rev/min. To offset the solventevaporation, additional solvent was slowly dripped into the millingslurry at a rate (˜1 drop/sec) as needed to maintain good milling flow.The slurry was milled at about 15° C. for approximately 5 hours. The inkconcentrate was diluted with an additional 50 g solvent and mixed forfew minutes before being separated from the milling media. Thedispersion was separated from the milling media by filtering themillgrind through a 10-20 μm KIMAX® Buchner Funnel obtained from VWRScientific Products. Particle size distributions were obtained ondiluted millgrind samples (about 50:1) using a Leeds & NorthropUltrafine Particle Analyzer (UPA). The results obtained are a 50% medianvalue. Particle size, as measured by UPA, are listed in the Table below.

Control Dispersion 1

A yellow dispersion was attempted to be made by mixing the followingingredients:

30 9.0 g Hansa® Brilliant Yellow 5GX-02 pigment (C.I. Pigment Yellow 74)(Hoechst Chem. Co.)

26.0 g Solsperse® 13,940 dispersing agent

50.0 g isopropanol carrier

87.5 g 50 μm polymeric milling media

The above components were mixed but not milled because the slurry wastoo viscous.

Control Dispersion 2

A magenta dispersion was attempted to be made by mixing the followingingredients:

7.2 g Magenta pigment (C.I. Pigment Red 122) Sunfast® Quinacridone (SunChem. Co.)

3.6 g Solsperse® 20,000 dispersing agent

60.0 g isopropanol carrier

87.5 g 50 μm milling media.

The above components were milled in a manner similar to that ofDispersion 1 except the milling blade tip-speed was changed to 7500 rpm.After 2 hours, the milling was discontinued because the slurry becametoo viscous. The results are shown in the Table below.

Control Dispersion 3

A magenta dispersion was attempted to be made by mixing the followingingredients:

10.0 g Magenta pigment RT243D (Ciba)

7.5 g Solsperse® 20,000 dispersing agent

50.0 g isopropanol carrier

87.5 g 50 μm milling media.

The above components were milled in a manner similar to that ofDispersion 1. After 1.25 hours, milling was discontinued because theslurry became too viscous. The results are shown in the Table below.

Control Dispersion 4

A yellow dispersion was attempted to be made by mixing the followingingredients:

9.0 g Yellow pigment (C.I. Pigment Yellow 74) Irgalite® Yellow GO

9.0 g Solsperse® 20,000 dispersing agent

40.0 g isopropanol carrier

87.5 g 50 μm polymeric milling media

The above components were mixed but not milled because the slurry wastoo viscous.

Control Dispersion 5

A magenta dispersion was attempted to be made by mixing the followingingredients:

9.0 g Magenta pigment RT243D (Ciba)

9.0 g Solsperse® 34,750 dispersing agent

60.0 g isopropanol carrier

87.5 g 50 μm milling media.

The above components were mixed but not milled because the slurry wastoo viscous.

Control Dispersion 6

A magenta dispersion was attempted by mixing the following ingredients:

9.0 g Magenta pigment (C.I. Pigment Red 122) Sunfast® Quinacridone (SunChem. Co.)

7.0 g Disperbyk® 140 dispersing agent (Byk Chemie USA)

40.0 g isopropanol carrier

87.5 g 50 μm milling media.

The above components were then milled in a manner similar to that ofDispersion 1 except that the milling speed was increased to 7800rev/min. The results are shown in the Table below.

TABLE Particle Size Dispersion Dispersant Pigment (nm) 1 Disperbyk ® 182Hansa ® Brilliant Yellow  15 5GX-02 (P.Y. 74) Control 1 Solsperse ®Hansa ® Brilliant Yellow * 13,940 5GX-02 (P.Y. 74) Control 2 Solsperse ®Magenta (P.R. 122) Sunfast ® 3600 20,000 Quinacridone Control 3Solsperse ® Magenta Ciba RT243D 2000 20,000 Control 4 Solsperse ®Irgalite Yellow GO (P.Y.74) * 20,000 Control 5 Solsperse ® Magenta CibaRT243D * 34,750 Control 6 Disperbyk ® 140 Magenta (P.R. 122) Sunfast ®1500 Quinacridone *Not measured

The above results show that use of the amine-terminated polyetherdispersant in accordance with the invention produced a dispersion withparticles having a particle size below about 100 nm, in contrast to thecontrol dispersants which. produced a dispersion with particles having aparticle-size above about 1500 nm or were not be measured because theslurry was too viscous to be milled.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

What is claimed is:
 1. A process for making an ink jet ink comprising:a) providing a dispersion containing a pigment, an alcohol carrier andan amine-terminated polyether dispersant; b) mixing the pigmentdispersion with rigid milling media having a particle size less than 100μm; c) introducing the mixture of step (b) into a mill; d) milling themixture from step (c) until the pigment particle size is below about 100nanometers; e) separating the milling media from the mixture milled instep (d); and f) diluting the mixture from step (e) to obtain an ink jetink having a pigment concentration suitable for ink jet printers.
 2. Theprocess of claim 1 wherein said amine-terminated polyether has thefollowing formula:

where R₁, R₄ and R₅ each individually represents a substituted orunsubstituted alkyl group having from 1 to about 6 carbon atoms; R₂represents hydrogen or a substituted or unsubstituted alkyl group havingfrom 1 to about 6 carbon atoms; R₃ represents a substituted orunsubstituted alkyl group having from 1 to about 10 carbon atoms or asubstituted or unsubstituted aryl group having from about 6 to about 10carbon atoms; x is from about 5 to about 100; and y is from 1 to about6.
 3. The process of claim 2 wherein R₁, R₄ and R₅ each individuallyrepresents methyl or ethyl.
 4. The process of claim 2 wherein R₂ ismethyl.
 5. The process of claim 2 wherein R₃ is a methyl-substitutedaryl group.
 6. The process of claim 2 wherein x is from about 15 toabout 45 and y is
 2. 7. The process of claim 1 wherein said dispersantis present in a ratio of dispersant to pigment of from about 0.1:1 toabout 5:1.
 8. The process of claim 1 wherein said dispersant is presentin a ratio of dispersant to pigment of from about 0.5:1 to about 2:1. 9.The process of claim 1 wherein said dispersion contains from about 0.1to 10% by weight of said pigment.
 10. The process of claim 1 whereinsaid alcohol carrier is isopropanol.